Fix That Leaking Battery

You own a C5 and you're probably concerned about the condition of its exterior, interior, and underhood area. While most of the C5s on the road are always squeaky clean, a hidden acidic force may be slowly destroying your prized possession.

We've discussed battery electrolytic acid leakage concerns in the past; unfortunately, the problem appears to be growing. Battery-acid leakage with any wet-cell battery has been a concern from the beginning. Side-terminal batteries have the additional burden of holding back the liquid acid. Although the side-terminal battery is not completely submerged in acid, it does have acid sloshing around it.

The lead side-terminal battery is bonded to the plastic case to prevent acid leaks. Rough handling can break the bond, and overtightening the battery-cable retaining bolt can break it as well. If the bolt is too long, it can crack the lead terminal, which allows acid to flow out of the bolt threads. Overheating a battery during charging can also damage the case and start a leak. This is evident if a battery case bulges out at all four sides.

Not only can the acid leak out of the terminals, it can also come out of the seam where the top and outer case bond together. Some products may stop the flow of leaking acid, but generally not for long. Some battery manufacturers pay for damages caused by leaking acid, but it's difficult to pinpoint whether rough handling or poor construction caused the problem.

In a C5, the concern is increased because a side-terminal battery sits on top of some important electrical components. There are multiple wiring harnesses below the battery, along with the PCM and TAC modules. There are also gray connectors next to the battery near the positive cable that are used to connect the various computers together. While all earlier Corvettes could be damaged from a leaking side-terminal battery, it wouldn't be the same catastrophic effect as in a C5. The acid tends to flow along the battery cable with the affected leaky terminal. Since a C5 leak is at the top side of the battery, it takes a lot of slosh to lower the acid level enough to damage the battery or affect its performance. So the damage will be slow and can be hard to detect.

A GM Corvette tech told us a chilling story of a leaking battery in a C5 that had a repair bill of $8,000. The acid destroyed multiple wiring harnesses and the TAC (throttle actuator control) module. Damage like this is certainly possible if the problem is ignored until the electrical components start to do peculiar things. We've had C5s in our shop with A/C concerns and found no vacuum to operate the mode doors. Further inspection and testing revealed that battery acid had destroyed the plastic vacuum lines that control the A/C system. In another case, battery acid was being drawn up the engine harness with engine vacuum. In these cases, the plastic vacuum line was replaced and wire-harness damage was minor and repairable. But even these repair bills ran between $400 and $800 because the battery and vacuum lines had to be replaced, the wiring harnesses repaired, and sheetmetal cleaning and refinishing was required.

The good news is, a C5 owner can spot the problem and address it before any major damage occurs. If you find a white powdery film on the battery-terminal retaining bolt or the outside of the battery cable, you have an acid leak. In some cases, the terminal retaining bolt and cable are clean, but there could be an acid trail down the battery below the terminal.

The question is, do you install another original-equipment battery or an aftermarket one? Do you change to a top-post battery? Installing a top-post obviously changes the OE look. It requires a positive and negative battery-cable change or cutting off the OE terminals and installing those hokey repair terminals.

Whatever you decide, install a Battery Mat first to soak up any leaking acid. The Battery Mat is a treated fiber mat that retains and neutralizes acid. But keep an eye on the terminals for that white corrosive powder because it's a warning that acid is likely permeating the battery cable and heading toward the starter.

A gel-cell battery is the best alternative. Optima and Exide have gel-cell replacement batteries that fit directly into a C5. The only concern could be the top terminals that come with the dual-terminal batteries. If your C5 has a dual-terminal battery, keep the covers on the top post terminals to avoid shocking or welding.

The benefits of a gel-cell battery outweigh its cost ($110 to $130), and the warranty is slightly better. Most have 84-month prorated coverage, with the first three years at no cost to the customer for replacement. Use the Web sites listed below for comparison and facts about the gel-cells.